As multiplexed optical analytical systems continue to be miniaturized in size, expanded in scale, and increased in power, the need to develop improved systems capable of delivering optical energy to such systems becomes more important. For example, highly multiplexed analytical systems comprising integrated waveguides for the illumination of nanoscale samples are described in U.S. Patent Application Publication Nos. 2008/0128627 and 2012/0085894. Further optical systems for the analysis of nanoscale samples, including the illumination and detection of such samples, are described in U.S. Patent Application Publication Nos. 2012/0014837, 2012/0021525, and 2012/0019828. Additional nanoscale illumination systems for highly multiplexed analysis are described in U.S. Patent Application Publication Nos. 2014/0199016 and 2014/0287964.
In conventional optical systems, optical trains are typically employed to direct, focus, filter, split, separate, and detect light to and from the sample materials. Such systems typically employ an assortment of different optical elements to direct, modify, and otherwise manipulate light entering and leaving a reaction site. Such systems are frequently complex and costly and tend to have significant space requirements. For example, typical systems employ mirrors and prisms in directing light from its source to a desired destination. Additionally, such systems can include light-splitting optics such as beam-splitting prisms to generate two or more beams from a single original beam.
Alternatives to the conventional optical systems have been described, in particular alternative systems having integrated optical components designed and fabricated within highly confined environments. For example, planar lightwave circuits (PLCs) comprising fiber interfaces, wavelength filters or combiners, phase-delayed optical interferometers, optical isolators, polarization control, and/or taps have been developed for use in telecommunications applications. In some cases these devices additionally include one or more laser sources and one or more optical detectors. The devices, which are sometimes also referred to as fiber spacing concentrators (FSCs), use integrated optical waveguides to route photons through an optical circuit, in much the same way as electrons are routed through an electrical circuit. They are fabricated using standard semiconductor fabrication techniques, and they can accordingly integrate both passive components, such as optical filters and fiber pigtail connectors, and active elements, such as optical switches and attenuators, during the fabrication process. As used in telecommunications equipment, they typically serve to couple and/or split optical signals from fiber optic cores, for the purpose of, for example, multiplexing/demultiplexing, optical branching, and/or optical switching. The devices thus provide the functionality of a more traditional optical train, while at the same time being significantly less expensive, more compact, and more robust.
In the just-described optical systems, an optical source and its target device are typically closely and permanently associated with one another within the system. For example, PLCs used in telecommunications applications are typically mechanically aligned and bonded to their laser light source and to their associated photodetectors during the manufacturing process. Such close and irreversible associations between an optical source and its target device are thus not well suited for use in analytical systems having a removable sample holder, where the optical output from an optical source, such as a traditional optical train, is normally coupled to the target sample holder through free space. In systems optically coupled through free space, the optical signal from an optical source needs to be aligned with a target device each time the target device is replaced, and the alignment can even need to be monitored and maintained during the course of an analysis, due to mechanical, thermal, and other interfering factors associated with the optical system. In addition, the integrated optical circuits typically used in telecommunications applications are not designed to carry the intensity of optical energy necessary to analyze the large numbers of nanoscale samples present in the highly-multiplexed analytical systems described above, nor are they designed for use with optical sources having wavelengths suitable for use in optical systems with standard biological reagents.
Another consideration in the design of an optical analytical system is the method of coupling of light from the optical source into the target device. For example, where a target device comprises an integrated optical waveguide for routing the optical energy through the device, launching of the optical energy into the waveguide can be unreliable and inefficient. Various optical couplers have been described to achieve this purpose, including the use of direct “endfire” coupling into a polished end of the waveguide, the use of a prism coupler to direct light into the waveguide, and the use of a grating coupler to direct light into the waveguide. Depending on the implementation, however, each approach has limitations with respect to efficiency, reliability, applicability, cost, and the like.
There is thus a continuing need to improve the performance and properties of integrated optical waveguide devices, particularly those that are reversibly coupled to external light sources. There is also a need to improve the performance and properties of optical analytical systems containing such integrated waveguide devices.